Mitsuo Tabata

Piezoelectrically Driven xyθ Table for Submicron Lithography Systems

A newly designed piezoelectrically driven XYθ table has been developed for submicron lithography systems. The XYθ table was fabricated using a monolithic plate structure, joined together with flexure hinges and driven by an inchworm function. This function involves the periodic clamping and unclamping of four blocks and the expansion and contraction of piezoelectric actuators. The XYθ table can travel a long distance with fine positioning in the X, Y, and θ directions. The velocities can be controlled up to 0.5 mm/s in the X and Y directions, and 0.3×10 −2 rad/s in the θ direction by changing the inchworm function stepping rate. Positioning accuracy of less than 1 μm in the X and Y directions, and 7.5×10−6 rad in the θ direction can easily be obtained using a servo system with a 0.5‐μm measuring resolution.

New Image Processing Hardwares And Their Applications To Industrial Automation

Image processing hardware, a high-speed image processor and an intelligent image memory unit, are presented and their applications to the industrial image processing are discussed. An image processor has been realized on the basis of local parallel computation architectures, which contribute to speeding up major calculations and to reducing the hardware cost and complexity. An image memory unit has been implemented to manipulate and display the image data with a highly intelligent control, which helps man-machine interaction to be effective. Although these processors are conceptually designed for general image processing purposes, several feasibility studies have revealed that they can be utilized as com-petent simulation tools for research works on shape recognition, particle measurement, real-time signal processing, etc.

Mask defect inspection method by database comparison with 0.25-0.35 μm sensitivity

Photomasks used in the fabrication of ultra-LSI (ULSI) circuits must be inspected for defects. For 256 Mbit dynamic random access read write memory (DRAM), it is necessary to inspect defects as small as 0.15 µ m. Moreover, inspection of defects of phase-shift masks is becoming an important task of an inspection system. This paper describes an automated mask inspection system (MC-100) based on die-to-database comparison, and a defect inspection method with 0.15 µ m sensitivity for edge and pindot defects. System configuration and the defect inspection method are discussed in detail, including the difficulties of defect detection in an attenuated phase-shift mask.

An electron beam image projection system with automatic wafer handling

Abstract A new electron beam image projection system has been developed for 0.5 μm lithography. The system features three newly-designed subsystems: a double Helmholtz-type superconducting magnet, an automatic wafer handling system and a mask-wafer alignment and parallelism control system. The system also has a high accelerating voltage operation capability. Practical resolution of 0.5 μm, wafer handling time of 120 seconds and alignment mark detection accuracy better than 0.03 μm in 0.1 seconds were attained.

A New Inspection Method for Phase-Shift Mask (PSM) on Deep-UV Inspection Light Source

As the mask pattern becomes smaller and more complex, the demand for a highly precise mask inspection system with high detection sensitivity and few false defects increases. In regard to inspection systems using a deep-UV wavelength, some issues have been encountered concerning inspection of an ArF-halftone (ArF-HT) mask, which is now entering practically used. In this paper, we report the defect detection sensitivity of Cr and KrF-HT masks, and discuss the issues concerning ArF-HT mask inspection and countermeasures to deal with them.

Newly developed mask inspection system with DUV laser illumination

A new mask inspection system for 150nm and 130nm semiconductor devices which utilizes a DUV laser of 257nm wavelength for an inspection illumination has been developed. A newly developed optical phase shift disk cancels the speckle nose caused by the high coherency of a laser. The phase shift disk has micro pits with different depth disposed randomly over the entire plate surface. The speckle pattern changes randomly by rotating the plate, and averaging pattern image by TDI sensor cancels the speckle noise of the laser illumination. Using this method, inspection of masks was realized at DUV wavelength.

High-resolution DUV inspection system for 150-nm generation masks

In order to perform mask inspection with the high reliability for 150 nm-rule and below devices, the inspection system with high resolution is indispensable. The phase shift masks like DUV HT masks must also be inspected with high sensitivity. A next generation mask inspection system MC-3000 which used DUV optics has been developed, in order to achieve these requirement. The wavelength of this optics is 257 nm that is shorter than that of current UV inspection systems, and is nearly equal to that of current DUV lithography systems. Short wavelength light and high NA optics obtain high resolution, so the defect detection of 130 nm or less is attained. The special issues for the DUV optics were solved by several new techniques. This paper reports the system configuration, basic characteristics for defect detection and inspection performances.

Detection of half-tone PSM pinhole with DUV reflected light source

The defect detection capability for a minute pinhole by a newly developed mask inspection system MC-3500 with DUV reflected light source is reported. The detection sensitivity of a minute pinhole less than 180 nm on a KrF phase shift mask (PSM) with transmitted light source is limited because the pinhole signal intensity is influenced by the diffraction light. The signal intensity of the pinhole both by the reflected light source and transmitted light source was calculated by an optical simulator, and the actual pinhole signal of the KrF PSM and that of the ArF PSM were measured using the MC-3500 with reflected light source. It was found that the 100 nm minute pinhole, which was not detected by the inspection with the transmitted light source, was detected by the inspection with the reflected light source. This shows the effectiveness of the reflective inspection, thus proved that the newly developed MC-3500 inspection system with reflective inspection capability has very high defect detection sensitivity for the advanced masks of 100-130 nm rule and below devices.

0.05 µm (3σ) Overlay Accuracy Through-the-lens Alignment in an Excimer Laser Lithography System

This paper presents a through-the-lens (TTL) alignment, called separated mark TTL alignment (SMART), applied to a KrF excimer laser lithography system. This SMART optical system does not require any complicated compensation mechanisms for longitudinal chromatic aberration. Several advanced methods for SMART optics to obtain higher overlay accuracy, such as optical heterodyne interferometry, real-time alignment system, and alignment signal processor, have been developed and adopted. The performance of such an improved SMART in an excimer laser lithography system was experimentally evaluated using dynamic random access memory (DRAM)-processed wafers. An overlay accuracy of 0.05 µm (3σ) has been achieved.

The effect of intensity distribution in the reflected beam on the detection error of monochromatic optical autofocus systems

The measurement error induced by the intensity distribution in the reflected beam from the surface of a substrate was studied to improve the focal accuracy of an autofocus system. It is shown that scanning of the probe beam across the wafer surface reduces the effect of nonuniform reflectivity. An accuracy of 0.6 μm can be obtained. A signal processing circuit which accommodates 40 dB of incident intensity range is developed.